Description
The following rules apply for single token:
The original situation is defined by the initial step. The sequence string contains 1 initial step only.
Only one step is ever active in the sequence string. The only exceptions are parallel branches in which one step is active per branch.
The active signal status processes take place along the directional links, triggered by switching one or more transitions. The direction of the string process follows the directional links and runs from the under side of the predecessor step to the top side of the successive step.
A transition is enabled if the steps immediately preceding it are active. Transitions whose immediately preceding steps are not active are not normally analyzed.
A transition is triggered when the transition is enabled and the associated transition conditions are satisfied.
Triggering a transition leads to the disabling (resetting) of all immediately preceding steps that are linked to the transition, followed by the activation of all immediately following steps.
If more than one transition condition in a row of sequential steps has been satisfied then one step is processed per cycle.
Steps cannot be activated or deactivated by other non-SFC sections.
The use of macro steps is possible.
Only one branch is ever active in alternative branches. The branch to be run is determined by the result of the transition conditions of the transitions that follow the alternative branch. If a transition condition is satisfied, the remaining transitions are no longer processed The branch with the satisfied transition is activated. This gives rise to a left to right priority for branches. All alternative branches are combined at the end by an alternative joint or jumps.
With parallel branches, switching a single transition leads to the activation of more than one step (branch). After this common activation, the individual branches are processed independent of one another. All parallel branches are combined at the end by a parallel joint. Jumps into a parallel branch or out of a parallel branch are not possible.